problem with line integral

hi, this is my problem:

i need to find the mass of the curve (which is shown in parametric form):

$\displaystyle x = e^tcos(t), y = e^tsin(t), z = e^t$

from $\displaystyle t=0$ to $\displaystyle t=a$

and the mass density of the line is reversely proportional to

$\displaystyle x^2 + y^2 + z^2$

and also $\displaystyle \rho (1,0,1) = 1$

i am having trouble with it - is reversely proportional means

$\displaystyle \frac{1}{x^2+y^2+z^2}$,

and if so what am is supposed to do with $\displaystyle \rho$?